1. Field of the Invention
The invention concerns a lifting magnet arrangement for controlling a pressure regulating valve or directional control valve.
2. Discussion of the Background
Lifting magnet arrangements are utilised for controlling hydraulic components, such as, e.g., switching valves or proportional valves, directional control valves or pressure regulating valves and sliding valves or seat valves. Fundamentally it is possible to classify them into structures including DC magnets and those including AC magnets, wherein armature switching is carried out in air ("dry" magnet) or in oil ("wet" magnet), respectively. I.e., the armature cavity is in the latter case filled with oil and relieved toward the tank. In proportional valves, so-called proportional magnets are used which belong to the group of DC lifting magnets and generate an output (force or stroke) which is proportional with the electrical input signal. Depending on a specific application purpose, classification is made into stroke-controlled magnets or force-controlled magnets, with the magnetic force being controlled in the latter by modification of flow while the stroke change may be disregarded, whereas in the former the armature position (stroke) is controlled.
FIG. 1 shows a view of a conventional lifting magnet arrangement including a thrusting actuating element, wherein a DC magnet switching in oil is employed.
A like lifting magnet arrangement 1 basically consists of a magnet housing 2 into which a pole tube 4 including a wound coil 10 is press-fitted. The pole tube one the one hand serves to limit the coil space, and as an axial termination of the housing on the other hand. This function is served on the other front side by a cover plate 8 which, in a given case (e.g. for intervention within the magnet force system), may also be divided into ring 9 and lid 8.
The magnet coil 10 may be connected to a current/voltage supply via a terminal 12 located on the housing 2.
The pole tube 4 includes an axial bore wherein an armature 16 is guided such as to be axially displaceable.
On its left-hand front side in the representation of FIG. 1, the armature 16 carries a tappet 18 which projects from the pole tube 4 in the axial direction and, in the shown embodiment, may be covered by a protective cap 20 (indicated by phantom lines in FIG. 1) for transporting purposes. The axial bore 14 is radially stepped back in the area of the tappet 18 in such a way as to form, depending on the construction, a guiding portion or at least a receiving space for the tappet 18.
On the other end portion of the armature 16 which is removed from the tappet 18, a coaxially extending rod 22 is fastened which projects into the cavity of the cover cap 8.
The front-side end portion of the pole tube 4 is formed by a stop member 24 which is screwed into the pole tube 4 and forms an axial stop for the armature 16. The rod 22 extends through the stop member 24 in a central position and comprises at its end portion 22 a threaded portion onto which a spring plate 26 is screwed as an armature-side abutment. A pressure spring 28 acts on this latter one, with the other end portion of the pressure spring 28 being supported on the adjacent front surface of the stop member 24 forming a housing-side abutment. The spring plate 26 (armature-side abutment) thus is arranged at a greater axial distance from the armature space than the axial stop (housing-side abutment).
By axial adjustment of the spring plate 26 along the thread at the end portion of the rod 22, it is possible to adjust the bias of the pressure spring 28 and thus the force biasing the armature toward the stop member 24.
Upon excitation of the lifting magnet, a force acts on the armature 16 to displace it against the bias of the spring toward the left (thrust direction) in the representation of FIG. 1 (stroke-controlled magnet) or builds up a magnetic force counteracting the pressure spring force without resulting in a substantial stroke (force-controlled magnet).
The axial bore 14, i.e., the armature space formed by it, the space encompassed by the protective cap 20, and the space enclosed by the cover plate 8 in prolongation of the pole tube 4 in which the pressure spring 28 is arranged (spring space), are filled with oil, with this oil space being connected to a tank port (not shown) via a conduit that is also not shown here, so that inside the lifting magnet a constant oil pressure (tank pressure) permanently prevails.
For the purpose of balancing and adjusting the force of the lifting magnet, or more precisely of the tappet 18 acting on the slide of the valve to be controlled (switching/proportional valve), the spring bias must be set in accordance with the force/stroke characteristic line of the magnet. For this setting process the cover cap 8 must be removed in the known valve arrangement, so that the oil contained in this space flows out of the lifting magnet arrangement 1. I.e., the pressure prevailing in the lifting magnet is not the predetermined operating pressure (tank pressure) but the environmental pressure (atmospheric pressure), so that the adjustment performed at atmospheric pressure may eventually be faulty at operating pressure, i.e., when the lifting magnet arrangement is filled with oil, and thus result in inaccuracies of valve control.
In contrast thereto, the invention is based on the object of furnishing a lifting magnet arrangement wherein simple adjustment at minimum expense in terms of device technology is possible without having to interfere with the hydraulic system.
This object is attained by the features of claim 1.
Due to the measure of making the adjusting means, which serves for changing the pressure spring bias by displacing the housing-side abutment, project from the housing of the lifting magnet arrangement in an oil-tight manner, basic adjustment may also be performed for a thrusting magnet without the housing of the lifting magnet having to be opened. I.e., during basic adjustment those pressure conditions which will also prevail during use of the arrangement are present on inside the lifting magnet. The force adjustment may thus be carried out with small expense in terms of device technology at substantially higher precision. In addition, due to permanent accessibility of the adjusting means, or more precisely of the actuating section of the adjusting means, it is even possible to quickly perform subsequent fine adjustment without having to disassemble the lifting magnet arrangement, so that the adjusting process may be carried out more easily, with more precision, more quickly in contrast with previous solutions, and free of oil. The latter circumstance results in cleaner assembly and reduced strain on the environment.
A particularly simple solution is obtained if the pressure spring is supported on an axial stop, the axial position of which may be changed by means of the actuating section which is accessible from the outside.
A particularly simple structure is obtained with the development in accordance with claim 3, according to which the actuating section has the form of a cap screwed into an inner bore of a bush-type stop member which constitutes a front-side termination of the lifting magnet housing.
The structural length of the lifting magnet arrangement in the axial direction may be reduced if the pressure spring is encompassed by the cap in portions thereof.
In the case where the axial stop and the cap are formed separate from each other, the axial stop can be biased against the cap by means of a spring member, so that axial separation of axial stop and cap can be prevented thanks to the action of the pressure spring. A particularly high pressing force on minimum space is obtained if a spring plate assembly is employed for biasing the axial stop.
As an alternative, it is also possible to form the axial stop integrally with the cap.
In an alternative embodiment, the axial stop may be connected to the mounting cap, with this connection preferably being effected by pressing.
An easy option for mounting an emergency actuation consists of an emergency actuation pin which is accessible from the outside and guided in the actuating section or in the adjustment cap such as to be axially slidable, whereby axial displacement of the armature may be brought about manually in the cause of a power failure.
Easy basic adjustment is possible if the basic position of the spring plate is adjustable on the spring rod.
As was already mentioned above, the lifting magnet arrangement according to the invention may be used for both stroke-controlled and force-controlled lifting magnets and is fundamentally suited for controlling switching valves and proportional valves.
Further advantageous developments of the invention are the subject matters of the remaining appended claims.